Gellan gum is an exocellular, microbial polysaccharide produced by Pseudomonas elodea and has been employed as a food additive. According to the FDA (21 CFR §172.665) gellan gum “may be safely used as a direct food additive for human consumption.” The structural formula for gellan gum has been studied extensively and reported to consist of repeating tetrasaccharide units with the following structure:
which can also be represented by:
-3-β-D-glcp-(1-4)-β-D-glcpA-1-4)-β-D-glcp-(1-4)-α-L-rhamp-(1-
wherein “glcp” designates glucose, “glcpA” designates glucuronic acid, and “rhamp” designates rhamnose.
Gellan gum is commercially available in a clarified form under the trade designation KELCOGEL® for foods and industrial products and under the trade designation GELRITE® from CP Kelco, A Huber Company, (J.M. Huber Corporation, Edison, N.J.) for microbiological media, plant tissue culture, and pharmaceutical applications. Gellan gum has the potential to form gels in situ in the presence of mono- or divalent cations.
Gellan gum microparticles may be useful in encapsulating both bacteria and drugs (see, for example, U.S. Pat. Nos. 4,822,534 and 5,516,543). However, these gellan gum formulations of the prior art result in low biodistribution of encapsulated material, a feature attributed to susceptibility of the gellan gum polymer to degradation, which could present potential toxicity problems for applications such as anti-cancer drug delivery.
The physiological environment of tumors necessitates drug delivery systems that are capable of maintaining a controlled-release profile in acidic conditions. Thus, better formulations of gellan gum with improved controlled-release characteristics are needed for active drug targeting in vivo.